Space discharge device and method of making it



T UN-I EDsTATES PA OF PatentedMar; 12, 1935 srAcE DISCHARGE nEvIcEMETHOD I or MAKINGIT *VictorO. Allen, Madison, N. J; assignor, by mesne'assignments, toRadio Corporation of America,

' a corporation of Delaware r No pr ing. Application April 4, 193b,

' fI'his invention relates to methods and means 51 members.

devices as audions, rectifiers, ;etc it is the usual I practicetoemployso called getters,.andclean-up agents itoj expedite the evacuation oithe devices :1 It has: alsobeen proposed to employ Chemical agents whichare left permanently within the device to act as'ikeepers so faras'occluded and residualzgases within the device are concerned.

Nothoroughly satisfactory single chemical; agent may beemployed as bothgetter. and fkeeperf with different types of electron emitters-.' I

heretofore to employ as a getter, magnesium.

. However the utility ofmagnesium is limited in a its advantagestodevices employing emitters of the thoriated tungsten type. In orderthatthe.

magnesium may' be rendered effective itis necessary'to subject it to aflashing operation whereby it becomes vaporized. Substantially the en-5"; tire. clean-up action of the magnesium is therefore eiiective onlywhile it is in a vaporized condition; Aside from this limitation thereisanother disadvantagewhich of course is common to all: vaporizablegetters, name y that it is difiicult n ztheiormof anon-transparentfmirror on the walls and other partsbf-the device. Ithasbeen{ .5;. proved'by many tests that after. the manufacture ot themagnesiumis almostentirely..-negligible} ci a deviceand while itds inuse theeffectiveness Devices have been actuallymade without employingthe magnesium. getter and said devices have been found to-possess asgood a life andoperating characteristics includingffreedom from gases aswith devices employing magnesium;

1 Accordingly it isyanothenimportant object of the present invention toprovide -a chemical agent or agents for; electron discharge devices and;possessing all the advantages of the usual 'jmagnesium getter andwithout the above noted and other disadvantages incident to the use ofmagnesium. v j y Another object of the invention is to; provide a -nove1chemical :clean-up agent for expediting '7 the evacuation'of electrondischarge deviceswhich agent'also acts asan effective .keeperf duringtheentire life of the device.

n Another object isto; providel a'nOnEVaporiZabIe.

I pjAnother feature of the invention relates to Applicantgis aware thatit has been proposed cal; agent capable tion not specifically enumeratedwill be appar-' billing with carbon dioxide, carbon monoxide;

Serial No.1 l41,703

14 Claims. "(o1.250+g'1.5);...

chemical agent which acts as an effective getter of manufacturing spacedischarge. devices and with particularity to a novel method of manufacturing devices employingwelectron emissiveand keeper while inthenon-vaporized state. Another object of the invention is to provide anovel typeof. clean-up agent having 'a' greater.

v g capacity to absorb or adsorb residual gases both 5. is well known inthe manufacture ofsuch V duringthe manufacture'and during the life ofthedevice. V l Another object of the invention is toemploy as a getteror clean-up agent thesame material which .canbe used for electronemissive pur 10 DOSES. V V r A feature of the invention relates to theuse of a compound of the alkali earthgroup and the alkali metal groupcontaining oxygen, as a getter and PkeeperF.

the'method of producing agetter and ;keeper within an electron dischargedevice.

7 Another feature of the invention relates to the method-of treatingacarbonate of the alkali earth group to produce'a chemical agent whichacts both as getter and keeperj g A further feature-of theinventionrelates to the method of producing a non-vaporized'chemiof acting as agetter" and keeper..- j 1 V a A further feature relates to, the methodof subjecting a chemical agent. within an electron discharge device tosuccessive treatments wherebysaid agent isfirst decomposed to produce anv oxide which acts as a cleanup agent and" also liberates the gas orgases acting to flush. out

any air or other gas within'the device.

V of the alkali or alkali earth groups to producean oxide. .bydecomposition without liberating any oxidizing gases or vapors. 7-.Other features and advantages of: the invenent after a considerationof the following detail; descriptions and the appended claims. 1

.It is a well-known fact that the oxides -of the V alkali earth grouphave a great affinity for com- Water; vapor and 'rnany other gases which'asis well knowninterfere with the proper evacuation and operation ofelectron discharge devices;

This characteristic is so marked that these oxides cannot be exposedunder ordinary; conditions to the atmosphere without being immediately.attacked; ,7 I j 1 i It is. also known that the addition of carbon tobarium or strontium carbonates considerably lowers the temperaturerequired for decomposition of such carbonates, and that during thisreaction carbon monoxide is liberated instead of carbon dioxide, as isshown by the following eq uation I In the manufacture of such devices.as audions or the like it is recognized that carbon monoxide gas being astrong reducing agentis an ideal gas for flushing out the devicebeforethe final clean up agent. vention therefore it is proposed to employ anyIn accordance with the-present insuitable salt either of the alkalimetal or the alkali earth groups.

of the invention; These salts are mixed withan organic material or anymaterial containing organic carbon either in the freeor 'associatedistates and subjected to heat. Thus in manufacturing audions, lamps, orvacuumtubes generally the following procedurehas actually been employedand found to produce very good re sults. A mixture of barium andstrontium carbonatesWit-h organic" carbon is mounted at any convenientpoint withintheenvelopeof the device. Preferably this mixture is mountedin the device at such a point that its temperature is not surlic'ientlyraised torenderit electronically active. Thus the mixture may becompressed within a small cup or container andfthis container mountedat'a distance from'the heater elementor filament off the device;

The device with the chemical thus mounted therein is placed on the pumpandfsubjected to simultaneously raised to a-relatively high ternperature, preferably by induced radio-frequency currents in-the usualmanner, and during this heat treatment the evacuation is continued andcompleted in the regular manner. When the evacuation hasbeen' proceededwith to-the re quired extent the device is'sealed oi? the pump.

Consequently. there is retained within the de-- vice a: comparativelylarge quantity of barium and strontiurn oxide which function'as-ke'epers' during. the actual life of the device: to react with gasesliberated from the elements and surfaces within the device. I r

From the foregoing it will be seen that there is produced a chemicalagent which acts during the initial stages of evacuation to expedite theevacuating time and also remains within the deviceto act as keeper andsince the keeping action of the agent is substantially entirelyindependent of its vaporization it is efiecthis at all times during thelife of the device regardless or the operating temperature thereof.

Inasmuch as the barium and strontium oxides resulting from thedecomposing process hereinabove described are themselves electronicallyemissive and are the same materials that are ordinarily employed forelectron emissive cathodes, it is necessary to mount the chemical agentsI For :example oxalatesor carbonates of barium and/or, strontium areparticularly advantageous in achieving the objects above described atsuch a point within the device that they do not become hot, to renderthem electronically active during the life of the tube. What is claimedis: V

1. The method of evacuating the enclosing envelope: of an electrondischarge device having an electron emitting cathode which comprisesheating apart from the cathode a stable salt of the alkali earth groupin the presence of a reducing agent to produce an alkali earth oxide,

subjecting'the envelope to a pumping operation during said heating, and'resubjecting the oxide 'to-heat to eifect a final evacuation.

2. The method. of evacuating an electron dis-- charge device having anelectron emissive cathode,. which includes the step of heating apartfromsaid'cathode, a carbonate of an alkali earth metal'i'n the presenceof a reducing agent with- .in the device:

3. The method of evacuating an electron discharge device-having anelectron emissive cathode which includes the' step of heating apartfrom-'sa-id cathode, a carbonate of an alkali earth metal inthe presence oforganic carbon within the device. 7 I v I 4.' The methodof evacuating anelectron dis charge device having an electron emissive cathode whichincludes thejstep of heating apart from said" cathode, a mixture orarium carbonate'in' the presence of'a reducing agent within the device:

5;. The-method ofevacuating an electron dis-' charge device having anelectron emissive cathode which includes the step of heating apart fromsaid cathode, a mixture of barium carbonate in the presence of organiccarbon within the device to reduce the barium carbonate to bariumpxideand then heating the barium oxide to complete the evacuation. V v

c 6. The method of evacuating an electron discharge device having anelectron emissive cath ode which comprises mounting a mixture of bariumand strontium carbonates together with organic carbon at a suitablelocation within the device where it will not be materially afiected"by-cathode heat, reducing said carbonates to their oxides, subjectingthe oxides to heat and simul-- taneously subjecting the device toexhaustion; j

7. The method of completing the evacuation'of a partially evacuatedelectron discharge device which comprises heatinga stable salt of thealkali earth group to liberate a quantity of carbon mon oxide within thedevice and to reduce said salt to the oxide, removing saidcarbon'monoxide, and then heating said oxide to effect a final clean-up.

8.- The method of completing the evacuation of a partially evacuatedelectron discharge device which includesheating a-carbonate of thealkali earth'group' to evolve a'quantity of carbon m'onoxide within thedevice and to reduce said salt to the'o'xidaremoving said carbonmonoxide,

' and then heating said oxide to effect a final cleanl Anelectron'discharge devi'ce'havingon' the interior thereof an electronemissive cathode and a separate quantity of a carbonate of the alkaliearth group situated within the device at a point where it will not bematerially affected by the cathode heat.

10. An electron discharge device having onthe interior thereof anelectron emissive member and a separate quantity ofmaterial apart fromsaid member comprising a mixture of barium and strontium'carbonates andorganic carbon.

1l. The method of evacuating an electron discharge device having anelectron emitting cathode which comprises mounting a mixture of anoxalate ofthe alkali earth group and organic carbon within'the deviceand subjecting said mixture to heatapart from said cathode;

12. The method of evacuating an electron'discharge device havinganelectronemitting cathode which comprises mounting a mixture of anoxalate of an alkali metal and organic carbon within the device andsubjecting said mixture to heat apart from said cathode.

13. The method of manufacturing an electron discharge device having anevacuated envelope which comprises subjecting a mixture of a salt of thealkali earth group and a reducing agent placed withinthe envelope toheat to effect a reaction therebetween to form an oxide of the metal ofthesalt' and carbon monoxide and evacuating the envelope during thereaction;

14. The method'of evacuating an electron discharge device having anelectron emitting cathode therein which includes the step of heating amix- 'ture of barium and strontium carbonates in the presence of organiccarbon within the device and apart from said cathode to efiect areaction there-- between to provide'barium and strontium oxides withinsaid device. VICTOR 0. ALLEN.

